These apparatuses find frequent application, often to replace fixtures with long fluorescent bulbs, in a continuous line or in separate bodies, in suspension, ceiling and recessed ceiling systems for interiors and built in to pavements and applied to walls for exteriors, in particular for illuminating façades, cornices, etc. In some embodiments, the linear boards accommodate and manage LEDs of different colours to implement RGB or CTC (Colour Temperature Change) lighting.
The LEDs mounted on these cards can be of various types but, to obtain high luminous power, high-power, mono- or multi-chip LEDs are normally used. The heat produced is concentrated in discrete points and requires the use of circuit boards printed on an aluminium substrate. The high cost of these boards is mainly due to the large aluminium surfaces of the printed circuit board.
For this reason, for some years boards have been proposed with “mid-power LEDs”, i.e., sources of much lower power and cost but with high lighting efficiency compared to high power LEDs. At the same total light emission of the board, mounted in greater numbers, these LEDs produce less heat and distribute it better to the printed circuit, thus allowing the use of insulating substrates such as simple Vetronite instead of aluminium. The cost per lumen is lowered significantly.
In many applications mentioned above, a major problem is that of uniformity of emission near the apparatus. For example, in the oblique illumination of a wall, excessive distances between the LEDs are to be avoided because they produce unwanted bright strips or visibly separated beams. More densely populated mid-power boards are advantageous for this aspect as well.
However, the short-step mounting of the LEDs can create significant problems in the case of collimating optics, i.e., to produce narrow beams.
Even from a linear board, one often wants to obtain a narrow beam in all directions. In this case, parabolic reflectors or collimating lenses (TIR, spherical or aspherical) on each LED generate beams that are narrower the larger they are; the limit to the use of this type of optical element is given by both the section of the apparatus and the distance between the lighting sources. In this case, therefore, the more populated boards are generally the most disadvantaged.
In the case of the uniform oblique lighting mentioned above, the light distribution should be fundamentally blade of light, narrow only in the direction transverse to the apparatus, as wide and uniform as possible longitudinally to it. To implement such a photometry with a row of LEDs (which are almost always Lambertian sources), one can choose various types of optics.